In indoor units of air conditioners, etc., cross-flow fans are often used in order to blow air. As pertains to a cross-sectional shape of a blade of such a cross-flow fan, an pressure surface of the blade and a suction surface opposite the pressure surface are curved along a direction of rotation of the fan further toward the outer side of the blade from a fan rotary shaft, and, near the center of the blade, are formed in an arc shape set apart from a straight line connecting an inner-peripheral part and an outer-peripheral part of the blade.
Conventionally, it is known that in blades in which the thickness distribution in the shape of the blade is configured such that a position of maximum thickness is located between a leading edge and a trailing edge, separation of flow at the leading-edge portion occurs, and turbulence readily occurs. In order to improve such an unstable flow when a high load is applied to the cross-flow fan, the blade structure disclosed in Japanese Patent No. 3661579 is configured such that the position of maximum thickness in the blade is at a location 4% of a chord length of blade from an inner-peripheral end, and the thickness decreases from the position of maximum thickness of the blade toward both end parts. However, in the blade structure disclosed in Japanese Patent No. 3661579, because the position of maximum thickness is at a location 4% of the chord length from an inner side, this position approximately coincides with the inner-peripheral end, and the thickness rapidly decreases toward an outer-peripheral end. Therefore, in some instances, after colliding at the inner-peripheral end, the flow quickly separates off due to the large curvature of the blade surface, and moves downstream in the separated state without rejoining at the outer-peripheral side of the fan on the near side relative to a blade-midpoint position.
In the blade structure disclosed in Japanese Laid-open Patent Application No. 5-79492, the thickness of the blade decreases further toward the outer-peripheral side of a fan so that the distance between blades in a direction perpendicular to a direction of airflow between the blades is substantially the same on the outer-peripheral side and inner-peripheral side of the fan. In the blade disclosed in Japanese Laid-open Patent Application No. 5-79492, when a load is applied, a flow vented out from the fan separates off, at a suction surface side having large curvature, in proportion with direction from an inner-peripheral end of the blade toward an outer-peripheral end of the blade, and readily gives rise to turbulence. Therefore, in the blade disclosed in Patent Document 2, an extremely unpleasant, intermittent abnormal noise referred to as “rustling” is readily generated due to the breakdown of a two-dimensional flow. Additionally, because the flow between the blades in Japanese Laid-open Patent Application No. 5-79492 readily gives rise to turbulence, abnormal noise (low-order narrowband-frequency noise (referred to below as “N noise”)) caused by rotation of the fan increases; this noise is projected at low frequencies, inhibiting a noise-reduction property. Furthermore, when a load is applied to the blade disclosed in Japanese Laid-open Patent Application No. 5-79492, blowing performance significantly deteriorates, and therefore cooling capacity and heating capacity of the fan decreases.